1. Field of the Invention
The present invention relates to a boring apparat us having an electric drill for forming a through hole in a workpiece such as a steel plate and, more particularly, to a boring apparatus wherein the electric drill supported by and moving reciprocally on a frame can be automatically moved to the return position at a high speed when the boring operation is finished.
2. Description of the Prior Art
When a through hole such as a bolt hole is to be formed in a plate-like workpiece such as a steel plate in a conventional boring apparatus, two operators must hold support rods for supporting the electric drill and push the press rods connected to the upper portion of the electric drill downward. Since two operators are required for the conventional boring operation, however, this results in an inefficient use of labor. In addition, the operators must push the press rods to form the hole, which can become very tiring, physically.
In order to solve the above problem, there has been proposed a boring apparatus which a single operator can use easily and efficiently.
With this boring apparatus, an electric drill having a tool spindle is supported on the front wall of the frame of the boring machine so as to move reciprocally in an axial direction of the spindle. In the frame, a reduction mechanism and a clutch which is engaged and disengaged according to the axial movement of a transmission shaft are provided between the drive shaft of an electric drill feed motor and the transmission shaft connected by manually rotatable arms. When the clutch is engaged by rotating the manual arms, the motor rotates the transmission shaft through the reduction mechanism to slide an electric drill supporting slide plate of the drill on the front wall of the apparatus frame in the axial directions of the tool spindle through the transmission shaft, gear and gear trains. To the bottom of the frame, an electromagnet unit is fixed to secure the frame onto the upper surface of the ferromagnetic workpiece such as a steel plate.
After the boring apparatus is placed in a predetermined position on the ferromagnetic workpiece, the electromagnet unit under the frame is magnetized to magnetically hold the frame thereon. As the electric drill is rotated and the feed motor is driven, the electric drill is moved towards the workpiece such that the rotating cutter forms a hole in the workpiece.
With the above conventional boring apparatus, the hole is automatically formed. When the cutting edges of the cutter reach the lower surface of the steel plate, however, the cutter must be manually pulled up. In doing so, the operator disengages the clutch and then turns the arms in the direction in which the transmission shaft rotates reversely to its feed direction. Thus, the electric drill is manually moved upward. Such a manual operation is time-consuming.
U.S. Pat. No. 3,371,257 discloses an electromagnetic base tool wherein the drill is fed and returned by means of electrical means. However, the switching from the feeding operation to the return operation is not made automatically but only manually, reducing the operation efficiency of the base tool.